The present invention relates to a method for fixing components to a pipe for circulation of a fluid forming part of a heat exchanger, in particular a condenser of an air-conditioning system.
It is known that air-conditioning apparatuses or systems comprise at least one pipe for circulation of a cooling or heating fluid, to which various functional components are associated. For example, in the case of condensers forming part of air-conditioning systems for motor vehicles, to one and the same tubular distributor there are rigidly associated one or more supporting brackets, fluid-inlet or fluid-outlet manifolds or connectors, a support for a filter, and similar components.
In order to obtain a condenser, the various components envisaged are preliminarly connected to the tubular distributor and are then definitively fixed thereto subsequently. Typically, the step of preliminary connection of the various components to the distributor, known as xe2x80x9ctackingxe2x80x9d, is carried out by arc spot-welding with weld material (namely, spot welding using a TIG or MIG process). The semi-finished product thus tacked together undergoes a brazing process in a special oven, with process temperatures in the region of 600xc2x0 C., in order to obtain definitive fixing between the various parts, which bestows the necessary mechanical strength on the assembly.
The present invention is based upon the realization that the known technique of tacking, obtained by spot welding, entails a number of drawbacks.
A first drawback is due to the difficulty of controlling the process in terms of regulation of the welding parameters. In this perspective, it should, for example, be considered that the aforementioned process is not exactly repeatable, in the sense that the weld spots carried out subsequently may have different characteristics from one another. This basically depends upon the changeable welding intensity (which in turn depends upon the welding current) and upon the possible presence of differences in thickness between the parts that are to be welded together.
In the case where the welding spots performed in the tacking step are of small dimensions, there is the risk that the spots will fail to withstand the high treatment temperature typical of the subsequent brazing process. Consequently, the functional component may detach from the respective distributor or tubular pipe and drop inside the brazing oven. On the other hand, in the case where the welding intensity is excessive, there is the risk of causing a perforation in the pipe, the said perforation being hard to detect in so far as the weld material collects inside the perforation itself. In the subsequent brazing step, however, the weld material may melt and thus be responsible for the onset of a leakage in the pipe, which may be detected only in a subsequent stage of the production cycle.
Other variables that further complicate the aforementioned welding process are then due to the difficulty of exact placing of the weld material, to the fact that the welding depth may prove non-constant, and to the fact that the quality of the connection between the parts may be impaired on account of the porosity of the welding spots. The welding process moreover presents problems due to deformation on account of overheating, which brings about geometrical modifications in the distributor, rendering the subsequent assembly thereof with the pipes of the exchanger difficult.
Another drawback of the prior art derives from the fact that, as has already been mentioned, the arc spot-welding process presupposes that the two parts that are to be fixed together should have thicknesses as close to one another as possible. Consequently, in practice the thickness of the various components to be associated to the fluid-circulation pipe is rendered congruent with the thickness of the latter (which is generally very small, typically in the region of 1.2 mm). This, however, is detrimental to the structural strength of the product, since also the corresponding supporting brackets must have a small thickness, at least in the points of fixing to the pipe. It is therefore evident that, in order to increase the sturdiness of the product, it would be possible to increase the thickness of the functional components, and hence also of the respective fluid-circulation pipe; however, this involves a considerable increase in consumption of material.
For the above reasons, then, control of the aforesaid welding process is extremely laborious, and thus slow and costly, in addition to entailing considerable consumption of electric power. Finally, it should be considered that the aforesaid process is very noisy and polluting, which renders it compulsory to use costly auxiliary sound-proofing systems and systems for aspiration of the welding fumes; moreover, the welding system itself is very costly.
From what has been set forth above, it is clear how the arc spot-welding process currently used for tacking the various functional components to the pipes of air-conditioning systems involves high process costs, as well as a high risk of production rejects.
The purpose of the present invention is to overcome the drawbacks of the prior art, and in this context the main purpose of the invention is to provide a method for fixing components to a fluid-circulation pipe forming part of a heat exchanger, in particular a condenser of an air-conditioning system, that is faster and more economical to implement, more reliable and more easily repeatable than the method currently employed according to the known art.
The above and yet other purposes, which will emerge clearly from what follows, are achieved according to the present invention by a method and a heat exchanger having the characteristics specified in the annexed claims, which are understood as forming an integral part of the present description.